For manufacturing containers made of divided molds, various methods are known. For this purpose, for example injection molding, blow molding or swaging are applied. In many cases, the divided mold serves a better removal or taking out of the formed object so that integral containers result. For swaging of sheets by means of pressure difference, mainly divided molds for the so-called twinsheet method are known such as described in EP-0 579 937 A1. Another kind of forming out of two die molds is described in DE-35 13 388 C2. The thus formed object is compressed along a fitting face of the die molds during the forming method and is welded around its contour. Openings in the molded object have to be introduced into the wall after removal from the mold, particularly for shapes of containers for filling and emptying. Among others, a corresponding method is known from DE-40 23 274 A1.
In order to avoid this additional working step it has already been tried to weld the joining member circumferentially between the flat sheet webs such that the thermally plastified sheets enclose the outwardly projecting part of the joining member and cooling down thereon dimensionally stable (DE-39 29 665 A1 and 29 29 665 A1). Alternatively, it is also known to undercut the flange-like enlargement of an outwardly projecting tube lug. In these cases it is assumed that the forming material encloses, in a flowable state, a joining member such that a welding results, because the sheet material can cool down dimensionally stable in the vicinity of the joining member. However, practice has shown that surface areas of connecting members not heated to be flowable do not form an intimate sealing welding connection, simply by enclosing, any intimate sealing welding connection with the sheet material heated to be flowable.
For smaller containers, the content of which is maximally 20 liters, which in the documents mentioned above is derived from, the described method for connecting the container to the joining members may be sufficient in many cases. However, as far as sealing connections of molded sheets with seal members are requested, which have to withstand high test regulations to transportation safety, the known methods for containers with a content of 30 to 1000 liters and more are not suitable. The method known from DE-39 40 497 A1 is also not sufficient, because there it is assumed that flowable material is flowing into a neck when the joining member is pressed thereon with its face side. This outside connection does not enclose in a sufficiently sealing way a flange member whatsoever type it may be. It is particularly referred to the fact that an enclosure of the pipe socket in the transition range of external pipe surface up to the seam further continuing in the container edge, form a slightly open lip. This is realized because the pressure relations are not sufficient for a closed seam formation in order to form the last portion of a nearly perpendicularly running semicircle.